1. Field of the Invention
The present invention relates to a disk drive, and more particularly to a disk drive including a servo writer function.
2. Description of the Related Art
Generally, a disk drive as typified by a hard disk drive is configured to record data on a disk medium (simply referred to as a disk hereinafter) by using a magnetic head (simply referred to as a head hereinafter) or reproduce data from the disk.
In the disk drive, servo information (a servo pattern) which is used to position a head at a target position (a target track or a target cylinder as a read/write object) on the disk is recorded on the disk.
As a disk drive manufacturing step, there is a servo write step of recording (prerecording) a servo pattern on the disk. By this servo write step, a servo track including a servo area in which a servo pattern is recorded is constituted on the disk. In the servo track, with a servo area being determined as a reference, a range immediately before a next servo area in a circumferential direction may be referred to as a servo sector in some cases.
On the other hand, with a servo track being determined as a reference, a data track is constituted as an area in which user data is recorded. The data track includes a plurality of data sectors (data area which serves as an access unit) belonging to respective servo sectors. Each data sector is identified based on a sector address (sector number).
As a servo write method, there is a manufacturing method by which a servo track is recorded on a disk in advance by using a dedicated servo track writer (STW) in order to increase efficiency of the servo write step, and the disk on which this servo track is recorded is assembled into a disk drive (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 4-337577).
In this manufacturing method, there occurs a state (disk eccentricity) in which the track center of servo tracks having a concentric circular shape formed on a disk in advance does not necessarily match with the rotation center of the disk (rotational shaft of a spindle motor). In an actual disk drive, since data tracks are constituted with servo sectors constituting servo tracks being determined as a reference, eccentricity is generated between the rotation center of the disk and the rotation center of the data tracks.
Thus, there has been proposed a disk drive in which an offset quantity corresponding to an eccentricity quantity between a track center of the servo tracks and a rotation center of the disk is measured in advance and an offset table for the eccentricity quantity is prepared on a memory (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-93083). This disk drive makes reference to an offset quantity from this offset table and executes a positioning compensation when controlling a head to be positioned at a target data track on the disk.
In this method by which the offset quantity is prepared in the memory, when the offset quantity is erased from the memory, the positioning compensation using the offset quantity is impossible. Further, a step of storing the offset quantity in the memory of the disk drive is required. Furthermore, in the head positioning operation of the disk drive, processing for constantly making reference to the offset quantity from the memory is required.